"""
Mutability -- Python Implementation
"""
class Mutability:
def __init__(self, is_immutable=False):
self._is_immutable = is_immutable
def _require_mutable(self):
if self._is_immutable:
raise ValueError, "object is immutable; please change a copy instead."
def set_immutable(self):
"""
Make this object immutable, so it can never again be changed.
EXAMPLES:
sage: v = Sequence([1,2,3,4/5])
sage: v[0] = 5
sage: v
[5, 2, 3, 4/5]
sage: v.set_immutable()
sage: v[3] = 7
Traceback (most recent call last):
...
ValueError: object is immutable; please change a copy instead.
"""
self._is_immutable = 1
def is_immutable(self):
"""
Return True if this object is immutable (can not be changed)
and False if it is not.
To make this object immutable use self.set_immutable().
EXAMPLE:
sage: v = Sequence([1,2,3,4/5])
sage: v[0] = 5
sage: v
[5, 2, 3, 4/5]
sage: v.is_immutable()
False
sage: v.set_immutable()
sage: v.is_immutable()
True
"""
try:
return self._is_immutable
except AttributeError:
return False
def is_mutable(self):
try:
return not self._is_immutable
except AttributeError:
return True
def __reduce__(self):
return Mutability, (self._is_immutable, )
